Commercial tires use a mph rating, not a letter rating like passenger tires. I haven't seen a tire faster then 75mph. On trucks with super singles, they are using wider based axles so to be able to run 0 offset wheels to keep the bearings happy. Good Luck, TomC

I don't know Tom I just saw a new bus Laughlin bought with Yokohama tires that had a Q rating I don't quite follow you about no letter all tires have a speed rating in letters my tractor tires have a speed rating of A2

The M rating is a 81 mph truck and bus tire those have been around for a long time, it makes no difference 65 to 70 mph is plenty fast for a bus but I have drove 80mph across Texas and was in the slow lane everything but the Amish passed me